What Causes Delayed Periods With Pregnancy Test Negative?

hi ama 27year old girl....i had a missed abortion in july last year...n then doc told me not to try for conception for next two cycles but we diidnt try till dec...after my dec cycle which was on 11th dec...we didnt use aprotection......i did not get my epriods this month am still waiting cause i did pregnancy test thrice n it came out to be negative....n now one of my gyanc friends ve suggested me to take regesterone to get the epriods n i why want to try for conception as well....wat do i do?